The present invention relates generally to the field of spinal implant systems, and particularly to systems that employ elongated spinal implants, such as rod and plates, connected at various locations along the spinal column. More particularly, the invention concerns a connection assembly that provides variable angle adjustability to the elongated spinal implant relative to a bone fastener engaged to the spine, independent of the adjustment of the bone fastener along the length of the elongated spinal implant.
Several spinal fixation systems have been developed for use in correcting and stabilizing sections of the spinal column and facilitating spinal fusion. In one such system, a bendable elongated spinal implant, such as a rod, is longitudinally disposed adjacent the vertebral column and then secured to various vertebrae along the length of the column by way of a number of bone fasteners of fixation elements. A variety of bone fasteners can be utilized, such as hooks or bone screws, which are configured to engage specific portions of a vertebra.
An example of one such system is the TSRH® Spinal System of Sofamor Danek Group, Inc. In this system, various hooks and bone screws are engaged to a spinal rod by way of eyebolts. In early versions of the TSRH® Spinal System, the vertebral hooks and bone screws were attached to the spinal rod at a fixed orientation, usually projecting perpendicularly below the rod. At the time, the TSRF® Spinal System presented a significant advance over prior systems in its VERSATILITY, strength of fixation, and ease of implantation.
However, one drawback faced by the original TSRH® Spinal System, as well as the other prevalent fixation systems, was that the surgeon was required to make significant adjustments to the contour of the bendable rod so that the bone fasteners could solidly engage the vertebra bodies. What was needed, then, was a bone fastener that could be connected to the spine at a variable angle. In order to address this need, the TSRH® Variable Angle Screw was developed, as described in U.S. Pat. No. 5,261,909. As shown in FIG. 1, this Variable Angle System 10 utilized the same TSRH® eyebolt 12 to achieve a connection between a bone fastener or screw 14 and a spinal rod R. In addition, the Variable Angle System 10 incorporated a washer 16 that fit over the eyebolt 12, engaged the spinal rod R within a groove in one surface of the washer, and provided a radially splined surface 18 facing the bone fastener 14. The bone fastener 14 had a complementary splined surface 20 so that the fastener could be situated at variable angular orientations relative to the spinal rod. A nut 22 threaded onto the post 24 of the eyebolt 12 clamped all the components together to complete the assembly.
The Variable Angle Screw system of the '909 patent presented a significant advance over prior rod-based implant systems. The system of the '909 patent was relatively compact and required a minimal number of parts, yet was able to accomplish a solid fixation of the bone fasteners to the rod at a wide range of angular orientations. One drawback of the system was that the eyebolt-nut combination tightened both the connection along the length of the spinal rod and the angular orientation of the bone fastener together at the same time.
A top-tightening assembly disclosed in U.S. Pat. No. 5,282,801 describes a clamp assembly 30, as depicted in FIG. 2, that replaced the eyebolt and nut with a clamp body 32 having a T-bar 34 against which the head of a variable angle bone fastener was clamped. In addition, while the original TSRH® System relied upon tightening a nut against the variable angle bone screw, the top-tightening approach of the '801 patent utilized a set screw 36 that acted against the spinal rod R disposed within channel 40 to push the spinal rod into the interlocking washer 38, and ultimately against a complementary splined face of the variable angle screw. With this system, the variable angle capability was retained, while a top-tightening feature was added. However, both the '909 and '801 patents describe assemblies that tighten and fix both the connection along the length of the spinal rod and the angular orientation of the bone fastener together at the same time.
With the addition of the top-tightening capability, the more recent TSRH® Spinal System has provided surgeons with a great deal of flexibility in the placement and orientation of bone fasteners, such as hooks and screws, relative to a spinal rod. The variable angle components greatly reduce the need to manipulate and bend the spinal rod to conform to the patient's anatomy. Even with the great improvements presented by the TSRH® Spinal System, certain surgical situations require the connection between the bone fastener and the spinal rod to be carried out in stages—i.e., locking the angular orientation of the bone fastener first, then fixing the connection along the length of the spinal rod, or vice versa.
One approach of achieving independent locking of the location of the bone fastener both along the length of the spinal rod and the locking of the fastener's angular orientation was a spinal implant device known as the Synthes Fixature Intern. This assembly, as described in U.S. Pat. No. 5,047,029, includes a threaded spinal rod over which a connector is placed between two nuts. On the connector there is a face spline clamp assembly for a Schantz-type screw. This device does not adequately serve the needs of spinal surgeons since the rods cannot be bent and still allow the nuts to be manipulated and it is difficult to place more than two bone fasteners on each rod, due to their size. There remains a need for a connector assembly that can accommodate various bone fasteners, while permitting locking the position along the spinal rod and the angular orientation of the bone fastener independently of each other, while addressing the drawbacks of the prior systems.